Couplers based on 5-pyrazolone compounds are extensively used for forming magenta dye images in silver halide color photographic materials. The 5-pyrazolone couplers however have an unwanted absorption in the yellow at about 430 nm and such secondary absorption sometimes causes color contamination. With a view to solving this contamination problem, 1H-pyrazolo[3,2-C]-S-triazole type couplers (i.e., couplers made of 1H-pyrazolo[3,2-C]-S-triazole derivatives) have been proposed in U.S. Pat. No. 3,725,067, British Patent Nos. 1,252,418 and 1,334,515, and Unexamined Published Japanese Patent Application Nos. 99437/1984 and 228252/1984. Couplers of this type are substantially free from the unwanted secondary absorption and, hence, are capable of eliminating the color contamination problem. Some couplers, if placed together with formalin (which is used in household furniture for pest control purposes), will experience decreases in density, but the 1H-pyrazolo[3,2-C]-S-triazole type couplers undergo minimum decreases in density in the formalin atmosphere. In addition to this advantage in terms of storage stability, these couplers have high sensitivity.
In spite of these advantages, however, the 1H-pyrazolo-(3,2-C)-S-triazole type couplers may sometimes experience undesirable variations in photographic characteristics such as increased fog density and varied sensitivity if the conditions of developing solutions are disturbed by, for example, variations in pH, agitation, or changes in the pH of the developing agent. It has also been found that these disturbances sometimes cause adverse effects on the image quality by increasing the graininess of the image.
With a view to solving these problems, the present inventors proposed a new technique in Japanese Patent Application No. 193609/1984 but the results were not completely satisfactory.